View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by UGD Academic Repository Geologica Macedonica, Vol. 27, No. 1, pp. 43–54 (2013) GEOME 2 ISSN 0352 – 1206 Manuscript received: May 10, 2013 UDC: 553.4.086:622.343(497.741) Accepted: October 17, 2017 Original scientific paper RARE MINERAL PHASES RELATED WITH MAJOR SULPHIDE MINERALS IN THE BUČIM PORPHYRY COPPER DEPOSIT, R. MACEDONIA Todor Serafimovski, Goran Tasev, Violeta Stefanova Faculty of Natural and Technical Sciences, “Goce Delčev” University, P.O.Box 201, MK 2000 Štip, Republic of Macedonia [email protected] A b s t r a c t: With the latest detailed mineralogical studies with polarizing optical microscope and microprobe analysis in the Bučim porphyry copper deposit were found and determined several representative and rare mineral phases, which have been composed metals from the gold-platinum group as well as those from the Cu-Bi-Se-Te-As group. In the bismuth-selenium of rare mineral phases were confirmed bismuthinite, galenobismutite, krupkaite, frie- drichite, emplectite, laitakarite and native bismuth, which represent new rare mineral phases in the Bučim porphyry copper deposit, as well as mineral phases of the Au-Pd group where clearly was confirmed presence of gold and pal- ladium with elemental mixtures representative for these mineral phases. It should be stressed out that both types of rare mineral phases were determined in pyrite and chalcopyrite from major ore parageneses in the Bučim deposit. The bismuth-selenium mineral phases are related to the major quartz-pyrite-chalcopyrite paragenesis, while Au-Pd min- eral phases are related with slightly higher temperature, oxido-sulphide parageneses such are magnetite-pyrite- chalcopyrite (Mt-Py-Cp) and pyrite-chalcopyrite (Py-Cp). Key words: ore minerals; gold-palladium phases; rare Bi-Se mineral phases; Bučim mine INTRODUCTION The Bučim porphyry copper is located within Cambrian gneisses and amphibolites (Čifliganec, the Bučim–Damjan-Borov–Dol ore region of Ma- 1993). cedonia, which is part of the well known Lece– Basic ore paragenesis was studied by Paviče- Chalkidiki metallogenic zone (Serafimovski, vić and Rakić (1983), Čifliganec (1993), Serafi- 1993), where manifestations of porphyry copper movski et al. (2006), and others. Beside the basic and epithermal ore are developed. On a more local ore paragenesis (pyrite, chalcopyrite, magnetite, scale the Bučim copper mine is located in eastern bornite, enargite, etc.), Bi-Se mineral phases and central Macedonia, 10 km west of the town of Ra- especially Au-Pd mineral phases were also deter- dovis. It is the only deposit of this kind in Mace- mined. Petrunov et al. (2001) published prelimi- donia that is currently being exploited and up to nary microscopic and microprobe data of the oc- date produced copper and significant amounts of currence of the platinum group elements (PGEs) by-product gold. The mine started production in within the Bučim porphyry copper deposit for the 1980 and produced four million tonnes of ore an- first time. An increased content of Pd as well as nually with 0.25% Cu, 0.27% Au, and 1 g/t Ag. Pd-mineralization (PGM) was established in the Estimated reserves are approximately 100 million Cu-Au ores of the deposit in Bučim, Macedonia. tonnes of low grade Cu-Au ores with some Ag and Thus, this is the fourth case in the territory of the Mo and include primary (the most important Cu- Balkan Peninsula after Bor-Majdanpek, Serbia Au resources) as well as secondary (related to the (Janković, 1990), Skouries, Greece (Tarkian et al., zone of oxidation-cementation enrichment) and 1991), and Elatsite, Bulgaria (Petrunov et al., mixed types of ores. The deposit is a porphyry 1992) where the Cu-porphyry style of hydrother- copper type deposit (Serafimovski et al., 1996) and mal PGM has been found. mineralization is related to Tertiary sub-volcanic As an alkaline porphyry deposit, the Bučim intrusions of andesite and latite in a host of Pre- deposit represents, beside copper, a significant 44 T. Serafimovski, G. Tasev, V. Stefanova gold resource for Macedonia and fits quite well (Economou-Eliopoulos, 2010) and bismuth-sele- into the recently reported elevated levels of PGEs, nium derivatives (Voudouris et al., 2013). With the particularly Pd and Pt, described in the Cordillera latest studies, results were obtained for Au-Pd- of British Columbia (Copper Mountain, Galore bearing pyrite and chalcopyrite as well as Bi- Creek), Allard Stock, La Plana Mountains, and Se±Au±Ag±Te minerals, which are the subject of Copper King Mine in the USA, Skouries porphyry this particular paper. deposit in Greece, Elatsite in Bulgaria, and so on GEOLOGICAL FEATURES OF THE BUČIM PORPHYRY COPPER DEPOSIT Geologically the Bučim deposit is located in (27.5–24.5 m.y., Serafimovski, 1993, or 24.5–24.0 gneiss, micaschists, and amphibolite, which make m.y., Barcikowski et al., 2012), subvolcanic latitic up the basement of the Serbo-Macedonian Mass and latite-andesitic bodies within Precambrian (SMM). During the Neogene, tectonic and mag- metamorphic rocks-gneisses, micashists, and am- matic processes resulted in widespread magma- phibolites. Primary Cu-Au mineralization occurs tism, which at the present erosion level is repre- around the subvolcanic bodies, being most abun- sented by sub-volcanic and volcanic facies of latite dant amid the hosting gneisses. Four ring-shaped and andesite in the form of dykes and necks. De- ore bodies (Central, Bunardžik, Vršnik, and Ču- tailed geological studies in the Bučim area have kar), are located within and around the magmatic demonstrated the presence of subvolcanic intru- bodies (Figure 1). Three ore bodies are morpho- sions which are of particular importance as regards logically related to stocks, and the fourth body is the spatial distribution of the copper mineralization presumably a fragment of a previously existing in the deposit. sheet-like layer of manto-type oxidized and rede- The ore deposition is genetically connected posited ore (Figure 1). with the intrusion of Tertiary, Oligocene-Miocene Fig. 1. Simplified geological map of the Bučim porphyry copper deposit (Serafimovski, 1993). 1. Central ore body; 2. Vršnik ore body; 3. Čukar ore body; 4. Bunardžik ore body Geologica Macedonica, 27 (1), 43–54 (2013) Rare mineral phases related with major sulphide minerals in the Bučim porphyry copper deposit, R. Macedonia 45 The main (Central) ore body is approximately tite, and cubanite. According to the results of ex- 500 m in diameter and 250 m in vertical extent and ploration, the copper mineralization covers an area has been worked in a large open pit. The ore con- of 1.5–2.0 km2 and is traced to a depth of 300 m. sists of 0.25% Cu, 0.27g/t Au, 1g/t Ag, 13g/t Mo, The country rocks adjoining the porphyry and 1–4% pyrite. The igneous rocks have been al- stocks are silicified, chloritized, and sericitized, tered to clays and micas. Important metallic miner- and underwent argillic alteration. Early potassic als are chalcopyrite, pyrite, and bornite, with small alteration developed as well (Čifliganec, 1993). amounts of galena, sphalerite, magnetite, haema- MINERAL ASSOCIATIONS More than three decades of study of this de- posit, in the following review we will give basic posit have shown that it is characterized by a com- mineralogical features of these two most common plex mineral assemblage and mineral paragenesis. minerals in the deposit. Numerous authors have studied mineral associa- Chalcopyrite is the most widespread ore min- tion in the Bučim deposit: Ivanov and Jasmakovski eral; at the same time it represents the principal ore (1970), Zarić (1974), Pavicević and Rakić (1983), mineral from the economic point of view. Its oc- Nevenić (1984), Čifliganec (1987), Serafimovski currence varies widely both in gneisses and mag- (1990, 1993); Serafimovski et al. (1990); Čifliga- matic rocks. Quantitatively it is less abundant than nec et al. (1997), Tasev (2003); Serafimovski et al. pyrite; exceptionally, at certain places it dominates (2006); Volkov (2010); Serafimovski et al. (2013); over pyrite in the samples collected from gneisses. Lehmann et al. (2013) etc. According those studies In andesites, chalcopyrite generally occurs in of listed authors, wide variety of minerals have traces. It has been developed in individual disper- been recognized in the Bučim deposit – both ore- sed grains rarer aggregates (up to 0.3 mm) and is bearing and gangue ones. The mineral composition distributed very unevenly throughout the principal of the orebodies explored so far does not substan- host rock. Exceptionally seldom it is intergrown tially differ, however there are certain peculiarities with pyrite or, still more seldom, with bornite. of mineral assemblages. Titanite, rutile, magnetite, Inside the Precambrian metamorphic complex hematite, chalcopyrite, pyrite, bornite, native gold, (gneisses), chalcopyrite occurs in the form of molybdenite, petzite, calaverite, and argentite were highly non-homogeneous, diffusive-dispersive dis- identified as ore minerals. Enargite, tetrahedrite, semination and sometimes forms nest to nest-veiny galena, and sphalerite are less abundant. Chalcocite concentrations. Chalcopyrite is, most typically, and covellite are predominant in the Čukar ore concentrated in the rocks exhibiting a pronounced body, being accompanied by pyrite, tenorite, and silicification and large proportion of femic miner- occasional native copper, malachite, and azurite. als. The ore mineralization was formed in the follow- ing sequence: titanite, rutile, and magnetite crystal- The size of dispersed chalcopyrite grains var- lized first, followed by pyrrhotite, cubanite, valleri- ies between some ten microns to 0.2 mm, ex- ite, and the early generation of chalcopyrite. After ceptionally up to 0.5 mm, whereas the size of ag- deposition of these minerals, the hydrothermal ore- gregates seldom exceeds 1.0 to 2.0 mm size. Chal- forming solution became enriched in sulfur, giving copyrite frequently hosts inclusions of silicates, rise to pyrite crystallization.